The present invention relates to combustion systems and particularly to an improved combustion tube for use in combusting a solid or liquid specimen to a gaseous sample for subsequent analysis.
In existing analyzers such as Model No. IR-33 sulphur determinator, commercially available from Leco Corporation of St. Joseph, Mich., the sulphur content of coal, coke, or other substances can be determined from a solid or liquid specimen which is positioned in an induction furnace and combusted to provide a gaseous sample. The gaseous sample is subsequently analyzed by an infrared detector detecting the sulphur dioxide concentration which is then displayed by a digital display as the sulphur content of the specimen. Certain aspects of the combustion system used in such prior art is disclosed in U.S. Pat. No. 3,923,464, issued Dec. 2, 1975, to Sitek, et al, and assigned to the present assignee.
Such systems are open ended and employ a carrier gas introduced into the combustion chamber of the induction furnace to oxidize the specimen and carry the resultant specimen gasses through the opposite end of the combustion chamber and through an infrared cell for detection. A closed loop combustion system of this general type is described in U.S. Pat. No. 3,985,505, issued Oct. 12, 1976, to R. L. Bredeweg, and assigned to the present assignee.
Although these systems provide excellent results in analyzing a specimen, coal cannot be heated directly with radio frequency energy used in these devices since it is a nonconductor. As a result, accelerating agents such as iron chips or powder or tungsten are required to be added to the sample. Further, the combustion chamber in such systems is relatively small and due to the fact that the coal is naturally combustible and creates an exothermic reaction during its combustion, it tends to sputter and some of the specimen can easily escape from the hot zone of the combustion chamber and not be broken down to provide an accurate analysis.
Horizontally extending combustion chambers of the open cylinder type are known in the prior art and represented by Leco Model No. 100 furnace. Although providing a resistance furnace not requiring sample material to be conductive and providing a large hot zone so that the materials cannot escape combustion, such prior art combustion systems were open at both ends and provided a flowthrough system. During operation, the ends had to be plugged to prevent escape of the specimen gas and/or admittance of ambient gasses. Such plugs naturally include the supply and exhaust conduits. This resulted in inconvenient operator access. Also, in the event that this type of system developed a leak in the combustion chamber, the positive pressure within the system could allow some of the specimen gas to escape and therefore not be analyzed. Also, with such systems, the delivery tube from the combustion chamber to the analyzer was spaced from the hot zone of the combustion chamber and recondensation of the specimen gas could occur reducing the amount of specimen being analyzed and thereby providing erroneous results.